1. Field of the Invention
This invention relates to power regulation. More specifically, this invention relates to control of a power source based at least in part on a power demand by a load.
2. Description of Related Art
FIGS. 1 and 2 show two conventional systems for power generation. In FIG. 1, an engine produces mechanical power that is inputted to a generator. For example, the engine may rotate a shaft that is coupled to the generator (possibly through a gearbox or transmission). The generator converts the mechanical power to electrical power that supplies a load. In response to an error between a predetermined engine speed output, and an actual engine output speed as measured by a speed sensor, a governor provides a command to a fuel supply controller, which controls the supply of fuel to the engine. Because the control of the engine is based upon the engine output speed, this type of control system may be called a speed reactive system.
A generator as shown in the system of FIG. 1 may produce electricity in either an alternating current (a.c.) or direct current (d.c.) form, depending on the requirements of the load. If a.c. is required, then the frequency of the current supplied by the generator must typically be regulated to within a small margin in order to avoid damage to the load. In the United States and Canada, e.g., a.c. current is typically maintained at 60 Hz. Because the rotational speed of the generator rotor determines the frequency of the electrical power produced, it is essential that the speed of the engine be regulated to a constant value.
Even if the load requires d.c. from the generator (possibly supplied via a rectifier or inverter), it may also be important to regulate the speed of the engine. In this case, the voltage of the d.c. output by the generator depends upon the speed of the engine. Although small variations in output voltage (i.e., ripples) may be filtered out, avoiding damage to the load will typically require that an average voltage output of the generator (and hence an average speed of the engine) be kept constant. That is, even though the pre-determined engine speed for a system according to FIG. 1 may yield good results over a broad range of conditions with respect to some criterion (e.g., minimal fuel consumption), one single value will typically be sub-optimal with respect to changes in such variables as pressure, temperature, and load power demand. Because fuel costs may account for 80% of the operating costs of such a system, increasing efficiency by even a few percent may result in a considerable cost savings.
Another shortcoming of speed reactive systems is that they operate without any knowledge of the power actually demanded by the load. Because the system reacts only to the engine output speed, its response is slowed by the inertia of the moving components in the power generation path, as no command with respect to speed may be met until the components are accumulated or decelerated as necessary.
FIG. 2 shows another system for engine speed regulation that is used, for example, in propeller-driven aircraft. In this system, it is also desirable to maintain engine output at a constant speed. An operator varies the power supplied by the engine to the load by commanding the final supply controller to adjust the supply of fuel to the engine. In order to maintain a constant engine output speed another controller varies the characteristics of the load. In response to a speed increase (possibly due to a command to increase power), for example, the controller may vary the pitch of the propeller, thereby increasing torque and maintaining a constant engine speed. For a given output speed, however, an engine will typically perform optimally (for example, with respect to fuel consumption) at only one particular power output value. Therefore, a control system as shown in FIG. 2 may also perform sub-optimally during much of its operation.
In a system, method, and apparatus for power regulation as disclosed herein, a load power demand value determines a power supply behavior that is optimal with respect to some criterion (e.g., fuel consumption). Such a system, method and apparatus also complies with load demand requirements more quickly and efficiently than existing approaches.